The invention relates to a bone nail, a tool for exerting a force or a torque, respectively, onto such a nail and an element for fixing the nail in the bone.
The principle of "bundle nailing" is described in the monograph entitled "Die Bundel-Nagelung" [Bundle Nailing] by K. H. Hackethal, Berlin, Gottingen, Heidelberg, 1961. This procedure results in a stable, true-to-form alignment of the marrow cavity by means of a plurality of elastic steel nails which are hammered in through an opening in the marrow cavity. The bundle of nails, which are usually bent, fills the marrow cavity completely or in part and, by spreading the nails in the region of the proximal end of the bundle, produces stabilization and thus maintains successful repositioning (idem, page 25, FIG. 13 and associated text). The bundle nailing process utilizes the spring effect of the nails which support themselves, inter alia, on the cortical part of the bone in the region of the window made for the introduction of the nails. Maintaining the initial tension in the nails after they are positioned is an important prerequisite for successful therapy.
All manipulations of the nails during insertion, positioning and extraction are made from their distal ends. Consequently, the following movements must be transmitted by way of the corresponding exertion of force:
1. insertion forces which act suddenly from the rear end of the nail in its longitudinal direction; PA1 2. torques which are produced during insertion and enable the nail to be twisted while being driven in; and PA1 3. retraction forces which enable the nail to be pulled out of the marrow cavity after the bone has healed.
The transmission of such forces requires special tools which must be of complicated design (idem, page 95, FIGS. 66 and 67) and which require space during use, a space which, due to the bundled arrangement of the nails, is available only to a limited degree.
German Auslegeschrift [Published Patent Application] No. 2,459,257 discloses a bone nail design which, according to the genus, has a distal end which is flattened in the form of a disc so that a plurality of nail ends can be arranged next to and above one another. The "disc-shaped flattening" offers the opportunity of transmitting torque during the insertion of the nail by means of a punch. This "disc-shaped flattening" is additionally intended to take care that the forces introduced into the bone as a result of the tension in the distal end of the nail are transmitted to the bone over an enlarged area.
Moreover, German Utility Model Pat. No. 7,519,604 discloses a bone nail having a region in the vicinity of its distal end where its cross section differs from the otherwise circular cross section of the nail for the purpose of introducting forces and/or moments during manipulation. The region of the nail deviating from the circular cross section has a concave face and a convex face which are curved predominantly about axes extending parallel to the longitudinal direction of the nail and in part extend beyond the nail's circular cross section. The nail is provided with a curvature and elasticity in such a manner that, when the nail is driven into the marrow cavity its distal end is supported by the cortical part of the bone.
This, last bone nail design however, does not consider that under surgical conditions it is not always possible to position the distal ends of the nails in such a manner that they rest smoothly against the cortical part of the bone; nor does it consider that the spring tension of the nail is introduced into the bone over the entire surface area of the flattened portion. Such optimum positioning is impossible in principle because the bundle nailing process is based on the principle that the tips of the nails spread out in space in the form of a fan along the trabeculae of the femur head so as to produce correct repositioning and stability of the fracture. Since the known nails having the disc-shaped flattened portions are provided with a curvature in the longitudinal direction of the nail, a curvature which is oriented in the same direction in all nails with respect to the flattened portions, there inevitably result positions for the disc-shaped flattened portions which deviate from a parallel shingle-like arrangement. This produces the danger that the narrow side of the flattened portion of the nails, which constitutes a sharp edge, exerts a chisel-like pressure onto the cortical part of the bone, thus raising the danger of perforation.
Since in their fixed state the distal ends of the nails project from the window opening made in the bone and utilize the edge of the window as a "back support", so that springing back into the marrow cavity is prevented, there exists the additional danger that, with less than optimum alignment of the flattened nail ends, these ends produce, in the region of their sharp edges, a skin ulceration with possible later infection.